1. Field
The present disclosure relates to 5-(2,6-dioxyphenyl)tetrazole-containing polymer, a membrane containing the same, an electrochemical device including the membrane and a method for preparing the same.
2. Description of the Related Art
In general, high temperature polymer electrolyte membrane fuel cells (HT PEMFCs) operate in the temperature range of 120-200° C. Gas streams are usually unhumidified but can also contain water if the cell is connected to a reformer.
Since no liquid water can exist under these conditions unless a very high pressure is applied, the electrolyte is usually based on phosphoric acid (PA).
In contrast to phosphoric acid fuel cells (PAFCs) where, e.g., an inorganic SiC matrix is used to immobilize liquid phosphoric acid (PA), the high temperature polymer electrolyte membrane fuel cells (HT PEMFCs) employ phosphoric acid absorbed in a dense polymeric membrane.
The most common membrane type is phosphoric acid-doped polybenzimidazole (FBI), in which PA interacts with the basic nitrogen atoms of the imidazole rings.
While only one phosphoric acid molecule interacts strongly with an imidazole ring, several more phosphoric acid molecules can be absorbed by hydrogen bonding. Up to 5-6 phosphoric acid molecules per imidazole can be doped when meta-PBI is immersed in an 85 wt % phosphoric acid solution at room temperature.
Membranes prepared by a sol-gel method, in which FBI precipitates out of a polyphosphoric acid (PPA) solution as the temperature decreases and polyphosphoric acid is hydrolyzed by ambient humidity to phosphoric acid, can even keep up to about 20 phosphoric acid molecules per imidazole.
So far, most of researches have been dedicated to PBI-based systems and there are only limited researches on alternative materials.
For example, aromatic polyethers incorporating pyridine moieties in the backbone have been studied.
Some researchers also reported that use of imidazole moieties as a side group in aromatic polymers or as part of radiation-grafted polymers.